Abstract
In prokaryotes, the protein protein N- and O-glycosylation pathways (GlyPW) have been experimentally characterised in some of the organisms. Identifying GlyPWs in other prokaryotes is essential to understand the role of glycosylation. Herein we report a BLASTp and a hidden Markov model (HMM)-profile based comparative genomics approach to identify putative O-glycosylation enzymes in completely sequenced prokaryotic genomes using the experimentally characterized O-GlyPW enzymes as query sequences. Homologs for enzymes of all five categories viz., initiation, modification, extension, flippase and oligosaccharyltransferase are found in 128 organisms and no homolog is found for any of these in 52 organisms. A large number of organisms have homologs for all categories except oligosaccharyltransferases, which show high sequence diversity. Thus, O-GlyPW enzyme homologs are widely prevalent. Most of the 128 organisms are proteobacteria and more than half are pathogenic. The pattern of distribution of homologs indicates species- and strainspecific variations and acquisition of homologs by horizontal gene transfer.
Highlights
The pathways for the glycosylation of proteins in prokaryotes have been characterized in some of the organisms and this include
In Neisseria meningitidis, PglE has been shown to be a β1,4-GalT and pglE has been shown to be responsible for phase variation between tri- and disaccharide structures [5]
Functional characterization of PglL from Neisseria meningitidis and PilO from Pseudomonas aeruginosa has shown that both these enzymes have relaxed glycan specificity and they require the glycan to be translocated to the periplasm [7]
Summary
The pathways for the glycosylation of proteins in prokaryotes have been characterized in some of the organisms and this include. These are glycosyltransferases (GTs) which catalyse the transfer of a saccharide from a nucleotide sugar donor substrate to acceptors in different linkages. These enzymes are responsible for the extension and elaboration of the lipid- linked glycan. Category-V includes oligosaccharyltransferases (OTs) which transfer the pre-assembled glycan from a lipid-1 In Neisseria, pgl denotes pilin glycosylation locus and contains enzymes of the. The identification of enzymes and characterization of their substrate specificities is critical to delineate the glycosylation pathways in various prokaryotes These help in understanding the role of glycans in processes such as virulence and pathogenesis. In the present study a bioinformatics-based comparative genomics approach has been used for the identification of the homologs of the enzymes involved in O-glycosylation pathways. The amino acid sequence of the ORFs has been used as query for all the database searches
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